Different designs of accumulator injection devices are disclosed in the following publications: Swiss Patent Specification 434,875; U.S. Pat. Nos. 3,464,627; 3,610,529; 3,680,782 and 4,545,352; German Published Application (Offenlegungsschrift) 3227 742 and corresponding U.S. Pat. No. 4,566,416; Published International (PCT) Application WO 78/00007 as well as in U.S. patent application Ser. No. 715,354; filed Mar. 25, 1985 and assigned to Stanadyne, Inc.
In the accumulator injectors disclosed in the above mentioned publications a certain amount of fuel is stored under high pressure in a chamber called accumulator, which is located in the injector body upstream of the seat of the injector needle valve. Downstream of this seat are located the injection orifices which communicate with the combustion chamber of the related internal combustion engine. At the beginning of the injection event the injector needle valve opens fast. Because of the fuel compressed in the accumulator a fast rise of the injected fuel rate from the injector into the combustion chamber occurs. This peculiarity of accumulator injectors is detrimental upon engine combustion; high combustion noise level and increased nitric oxide emissions being the result of this fact.
In order to get those conditions under control it is necessary to slowly increase the rate of the injected fuel flow at the beginning of the injection event, which can be achieved if the injector needle valve opening motion can be controlled. Furthermore the slower injector needle valve opening motion shall not influence its closing motion, which should be as fast as possible, again for improved combustion. This taylored opening and closing behaviour of the injector needle valve, together with the choice of the type of injector tip and injection holes brings about a desired shape of the injection rate; the process of controlling this property is called "rate shaping".
An injector design is simple if the number of tight fits and lapped surfaces are minimized. The same is valid for the number of injector components and for their geometry, which should be easily machinable. In addition it is important that the injector may be assembled and calibrated to its correct mode of operation on an automated calibration machine.
The main purpose of the present invention is to disclose new and improved design solutions which allow to control the opening and closing motions of the injector needle valve. In addition, the present invention aims to provide injecting devices which are more simple in construction and thus less expensive to be manufactured compared with the prior art solutions.
Advantageous embodiments of the invention are discussed in the description below and shown in the drawings.